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Description
M5-M12 thread repair kit – technical data
Case contents and thread insert specifications
| TECHNICAL DATA | |
|---|---|
| Threads repaired | M5, M6, M8, M10, M12 |
| Thread pitches | 0.8 / 1.0 / 1.25 / 1.5 / 1.75 mm |
| Thread inserts | 75 pcs (15 per size) |
| Insert length | 1.5xD |
| Insert material | stainless steel |
| STI taps | 5 pcs, HSS |
| Drill bits | 5 pcs, HSS, Ø5.2–12.4 mm |
| Installation tools | 5 pcs, tool steel |
| Tang break-off tools | 5 pcs, tool steel |
| Total pieces | 95 |
A stripped thread in a gearbox housing, pump housing, or aluminum cylinder head does not necessarily mean replacing the entire component. The Varel M5-M12 thread repair kit contains everything needed to restore the five most common metric threads: drill bits, STI taps, installation tools, tang break-off tools, and 75 stainless steel inserts. Repairing a single hole takes around a quarter of an hour and usually does not require removing the assembly from the machine.
Case contents – 95 pieces for five thread sizes
A complete set of tools and inserts in one package
RANGEM5 – M12
INSERTS75 pcs
LENGTH1.5xD
INSERT MATERIALStainless steel
KIT CONTENTS
| ▸ | HSS STI taps M5, M6, M8, M10, M12 – 1 pcs each |
| ▸ | HSS drill bits Ø5.2 / 6.2 / 8.3 / 10.3 / 12.4 mm – 1 pcs each |
| ▸ | Insert installation tools No. 5, 6, 7, 8, and 10 – 1 pcs each |
| ▸ | Tang break-off tools – 5 pcs |
| ▸ | Stainless steel 1.5xD thread inserts – 75 pcs |
| ▸ | Case with compartments for tools and inserts |
A thread insert, commonly called a helicoil, is a resilient coil wound from diamond-section wire. The outer edge of the wire engages the oversized thread cut with an STI tap, while the inner edge restores the nominal thread for a standard screw. The screw size remains unchanged, so there is no need to switch to a larger thread or modify the mating component. The stainless steel insert wire has a tensile strength of Rm ≥ 1400 N/mm², so a repaired thread in aluminum can be stronger than the original.
Drill bits and STI taps – hole size for each insert
Drilled hole diameters and insert heights for all sizes
Drill bit diameters and insert heights for M5-M12
| Thread | Pitch P [mm] | Drill bit for insert [mm] | Drill bit for standard thread [mm] | 1.5xD insert height [mm] | Inserts in kit |
|---|---|---|---|---|---|
| M5 x 0.8 | 0.8 | 5.2 | 4.2 | 7.5 | 15 |
| M6 x 1.0 | 1.0 | 6.2 | 5.0 | 9.0 | 15 |
| M8 x 1.25 | 1.25 | 8.3 | 6.8 | 12.0 | 15 |
| M10 x 1.5 | 1.5 | 10.3 | 8.5 | 15.0 | 15 |
| M12 x 1.75 | 1.75 | 12.4 | 10.2 | 18.0 | 15 |
The hole for an insert is considerably larger than that for a standard thread of the same size because it must accommodate the wire thickness on both sides of the profile. The STI thread diameter is calculated as the nominal diameter plus 1.3 × pitch: for M10 x 1.5, this gives 10 + 1.3 × 1.5 = 11.95 mm. Hence the 10.3 mm drill bit instead of the 8.5 mm bit used when cutting a thread directly in the material. Drilling also removes all damaged threads, so the quality of the repair does not depend on the condition of the old thread.
Repairing a stripped thread step by step
Four operations with the same set of tools
Process thread repair step by step
1Drilling the hole
Drill bit for M10: Ø10.3 mm
2STI tapping
Coolant: required
3Screwing in the insert
Recess depth: 1/4–1/2 of a turn
4Breaking off the tang
Tool: tang break-off tool from the kit
✓Thread ready
Class: 6H
The sequence is identical for all five sizes — only the tool diameters change
Before tapping, chamfer the hole entrance and guide the tap perpendicular to the surface, because an angled insert causes the screw to bind. After installation, the top of the insert should sit 1/4 to 1/2 of a turn below the surface: a protruding insert interferes with the screw head, while one installed too deep reduces the effective thread length. Remove the broken tang from a blind hole.
▲
Application limitation
The inserts in this kit have a length of 1.5xD — this is standard for steel and cast iron. In aluminum, magnesium alloys, and plastics subjected to full tightening torque, use inserts 2xD–3xD, available separately. A standard tap one size larger cannot produce an STI thread: its diameters differ, and the insert will not hold in the hole.
The M5-M12 thread repair kit covers the sizes most frequently stripped in the workshop: from M5 in accessories and covers to M12 in engine and suspension mounts. Once the insert is installed, the hole accepts a standard screw of the same size, and 15 inserts per size provide enough for a dozen or so repairs without purchasing separate kits.
Frequently asked questions about thread repair with inserts
Selecting the drill bit, insert, and tools
Frequently asked questions
A Ø8.3 mm drill bit, which is 1.5 mm larger than the 6.8 mm bit used for cutting a standard M8 thread. This drill bit is included in the kit, along with 5.2 / 6.2 / 10.3 and 12.4 mm bits for the other sizes.
No. An STI tap has the same 60° thread angle and the same pitch as the target thread, but its diameter is increased by approximately 1.3 × pitch — for M10 x 1.5, this is 11.95 mm, not M12. The insert will not lock in a thread cut with a standard tool and will unscrew with the screw.
The kit contains 75 stainless steel 1.5xD inserts — 15 pcs for each of the five sizes. The same taps and tools also accommodate 2xD, 2.5xD, and 3xD inserts with the same thread, sold separately.
It is usually stronger. In a thread cut directly in the material, the first three threads carry approximately 87% of the load, while the resilient insert distributes it more evenly — the same threads then carry approximately 69%. The screw remains standard because the inside of the insert restores the nominal thread to class 6H.
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Shipping
All orders are delivered by courier company GLS. For orders exceeding 369 PLN gross shipping is FREE
| Courier GLS | Przelew24 / Prepayment | 14,76 zł gross | Delivery time 1 working day |
| Courier GLS | Cash on delivery | 17,26 zł gross | Lead time 1 working day |
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